1. Field of the Invention
This invention relates to an electrical connector shell, and in particular to a die cast electrical connector shell including an integral shield and integral cable gripping teeth. The invention also relates to a shielded electrical connector of the type used to terminate a cable having a braided outer conductor, and in particular to a shielded electrical connector having improved braid-to-shield continuity and an improved contact arrangement. Finally, the invention also relates to a contact arrangement for an electrical connector which eliminates the need for a dielectric contact housing structure.
2. Discussion of Related Art
Cables made up of multiple individual wires surrounded by a braided outer conductor are used as data buses in computer applications. The cables are terminated by means of connections surrounded by a metal shell, the shell being electrically connected at the rear to a braided outer conductor and at the front to a shield which surrounds the connector contacts and establishes and electrical connection with the shell or housing of a mating connector or component, and the wires are terminated by a contact structure which includes a dielectric support and contacts extending through an opening between the metal shell and the front shield.
The purpose of the electrical connections between the cable braid and connector shell, and between the shell and contact shield, is to provide shielding continuity and prevent leakage of radiation generated by signals carried by wires in the cable and the contacts extending from the metal shell to the shield.
There are generally two areas in a conventional data bus connector where shielding continuity may be disrupted. The first at the seam between the relatively thick metal shell which houses the cable termination and the thinner front shield which surrounds the contacts and establishes electrical contact with the corresponding mating connector or component. While elimination of the seam between the connector shell and front shield in this type of connector has not previously been addressed, various alternative cable braid termination arrangements have been used or proposed.
The usual practice for terminating the cable braid to the connector shell is to use a crimp ring method, in which the crimp ring is compressed in the rear passage of the backshell to establish electrical continuity between the shell and cover and provide strain relief, or to use either a separate staple which is driven down over the braid or a clamp which is placed over the braid and secured by two screws. These termination methods are relatively costly and complicate the assembly process, however.
A simpler cable termination arrangement is disclosed in U.S. Pat. No. 5,244,415 (the '415 patent). The connector described in this patent consists of a die cast metal backshell made up of a base and cover, a rear section having integral cable gripping structures extending into a passage through which the cable enters the shell, and an opening at the front side of the die cast shell for receiving a thin wall trapezoidal shield member which accommodates the contacts and is mated with a corresponding connector or component housing.
More specifically, termination of the die cast metal shell to the outer braid of the cable is accomplished in the connector of the '415 patent by means of ribs extending inwardly from a wall in the base and tabs depending from the upper at a position between the ribs to form a passage into the chamber, the distance between the ribs and tabs being narrower than the normal diameter of the outer braid so that the outer braid is compressed horizontally by the ribs upon placement of the cable between the ribs of the base, and compressed horizontally by the tabs and vertically by the upper and lower walls of the passage formed upon attachment of the cover to the base, establishing an connection between the braid and the backshell and providing strain relief. To improve electrical continuity, the '415 patent depicts placement of a ring of copper foil, described as being optional, around the cable braid in the area of termination.
The present invention replaces both the conventional crimp ring, staple, or foil cable braid termination arrangements and the arrangement disclosed in the '415 patent, and also addresses the problem of shielding continuity at the seam between the metal shell and the thin wall front shield, by integrating into the metal shell a set of offset cable gripping teeth as well as the front shield. The offset cable gripping teeth are arranged to deform the cable braid to establish a low resistance electrical connection while at the same time minimizing stress on individual wires in the cable, reducing the problem of short circuits or unacceptable impedance changes in the signal-carrying wires, while integration of the front shell establishes a completely seamless path between the cable braid termination and the mating portion of the connector to eliminate resistance and RF leakage at the metal shell-to-shield interface. In addition, the present invention provides an improved contact arrangement which is especially suitable for use in such an electrical connector, and which does not require a dielectric housing structure for the contacts.
There are of course electrical connectors in which a mating front portion is integral with the rear portion of the connector, including cylindrical connectors, BNC connectors, and so forth. However, connectors of the type employing a thin wall front shield have consistently used a separate shield, as described in numerous patents, including the '415 patent and U.S. Pat. Nos. 4,678,256, 4,689,728, 4,786,260, 4,822,304, 4,854,890, 4,921,441, and 5,108,294, all of which disclose cable connectors having discrete or separate trapezoidal shield arrangements, rather than integral front shields, and which therefore cannot provide optimal electrical continuity between the outer conductor of the cable and the shield.
Also known are electrical connectors which include cable gripping teeth arranged to deform the outer jacket of a cable, as in the present invention, and connectors with offset cable gripping structures. However, the advantages of combining integral cable gripping teeth and offset cable gripping structures does not appear to have been previously recognized, and particularly not in the context of a metal connector shell for a shielded multiple wire cable.
Typical of the previously disclosed offset cable gripping structures is the one disclosed in U.S. Pat. No. 4,640,984 (the '984 patent). While the cable gripping structures described in this patent are offset from each other along the axis of the cable, as in the present invention, the cable gripping structures are not cable gripping teeth arranged to deform the cable, and the context in which the gripping structures are disclosed is not that of a connector shell. Instead the cable gripping structures described in the '984 patent are used in a strain relief structure in which the cable is intentionally bent to form a serpentine path which retains the cable. The cable gripping structures of the '984 patent do not have the function of providing an electrical connection between an outer cable shield and the housing of the device, and the cable disclosed in the patent is a flat cable for which stresses on the inner wires are apparently not considered a problem. In contrast to the purposeful bending of this type of strain relief, which substitutes for cable penetration, the present invention keeps overall bending of the cable, as it traverses the passage into the shell, to the minimum necessary to ensure electrical contact and strain relief.
On the other hand, in cases where the connector is provided with teeth arranged to penetrate the cable, the teeth are not integral with any portion of the connector housing, and offsets are not used. Examples of patents showing cable gripping teeth which penetrate the cable include U.S. Pat. Nos. 2,519,726, 3,375,481, 3,909,101, 4,293,180, 4,363,531. Because the teeth are designed to penetrate the outer insulating jacket of the cable, rather than a braided outer conductor, shielding continuity is not a consideration.
Finally, it is also known to use circuit boards as part of the wire termination arrangement, but the conventional circuit board termination arrangements all require the use of additional dielectric support structures, which raise the height of the front portion of the metal shell and complicate assembly. In contrast, the improved contact structure of the present invention, which involves providing solder pads on a circuit board to which the individual wires of the cable are directly soldered, and a contact grid also formed on the circuit board to which the solder pads are connected by traces, is supported by integral support structures in the shell itself and requires no additional support elements.
In summary, none of the prior connector arrangements discussed suggests a cable connector of the type having both a metal shell to which the outer braid of the cable is electrically connected and a thin wall contact shield, which is capable of providing a continuous low resistance electrical ground path from the outer cable conductor all the way to the shield, with no seams and thus optimal electrical properties, and which eliminates the need for a dielectric contact support structure. In all of the prior connectors of the type with which the invention is concerned, the thin wall shield is a discrete structure from the metal shell, and none of the prior connectors includes integral offset teeth arranged to deform the outer braid of the cable and thereby minimize the resistance of the braid-to-shell interface while at the same time minimizing stress on individual wires within the cable.